Too frequently acquiescing to poor chair design results in discomfort and undesirable, if not debilitating, back and muscle pain. The situation is exacerbated in the case of the infirm who must spend prolonged periods in beds or chairs ill suited to their needs for comfort, mobility, and motion. The object of the present invention is to meet these needs.
The present invention distinguishes itself from prior art in the following areas: meeting criteria for good chair design, customization to fit users of both sexes, use of a 3rd class level to raise and lower backrest responding to seat movement, having the capacity to be folded and disassembled, providing a customized surface that contours to the occupant, and providing use of various ground engaging components, including rockers, to alter seat angle.
Henry Dreyfuss Associates and Dr. Janet Travell have specified characteristics of good chair design and compiled anthropometric data to support such design. Their studies and a summary thereof by Alan marks reveal:
1) A contoured seat even if it faithfully reproduced body shape is not comfortable. The smallest shift in position causes misalignment. The most comfortable contour is the ever changing one made by the sitter adjusting position on a cushioned surface. A way to deal with fatigue is to allow for movement rather than locking muscles into a single, tiring position.
2) If seat angle is less than 15 degrees and the backrest angle is more than 120 degrees, then the body tends to slide forward causing discomfort.
3) An excessively long seat comes in contact with the back of the leg and forces the occupant to slide forward away from the backrest resulting in discomfort. High seat pressure at the seat front edge slows blood circulation to the legs and causes undue pressure on nerves in the thigh. Too short a seat length, though, fails to provide adequate seat support under the thighs. Load on other tissues consequently increases.
4) A backrest that fails to maintain the natural curvature of the back induces backaches.
Prior art indicates that reclining chairs for the infirm, particularly those serving as beds, do not meet Dreyfuss' and Travell's requirements for good chair design. In particular they usually do not provide a variety of seat inclinations approaching 15 degrees, and thus are inherently uncomfortable and unsuited for prolonged occupancy in the chair-like position.
In the bed-like position the utility of such chairs is frequently diminished because: 1) they provide discontinuous support in the leg, seat, or back regions, and/or 2) they elevate chair level from the usual sitting level to a very high and inconvenient position corresponding to a hospital stretcher.
As distinguished from the common chair, a chair converting into a bed must support all principal body segments (leg, seat, and back) in a wide variety of positions. Its elements must consequently hinge at points conforming with precision to the length of the particular occupant's body segments. The need for a custom fit is a point on which the utility of the chair depends. Without a custom fit, it will be uncomfortable and unsuitable for prolonged occupancy. In so far as I am aware, prior art does not reveal a systematic inventive concept: 1) to meet the above requirements for a custom fit in reclining chairs used also as beds, or 2) to disclose a process for manufacturing chairs so designed.
Anatomical differences between men and women are sufficient to challenge customization. Using the technique of linear regression analysis, I found that where "x" is body height and "y" is lower leg length, the formula 0.3174.times.-2,1298=y explained the relationship between height and leg length of a typical sample of males and females with a correlation coefficient of 99.97%. However, no such singular accurate formula appeared to explain the relationship between heights and seat lengths. Women tend to have a longer seat length than men of equal height and consequently also require a shorter backrest. Additionally mature females are on average 5 inches shorter than males. Females currently comprise 64.4% of the population using wheelchairs.
The implications for customizing chairs convertible to beds are that: 1) separate male and female Tables must be used to suggest appropriate back, seat, and leg segment lengths, and 2) that the process of manufacture must separately anticipate the quantities of chair segments of discrete sizes required by males and females. The process revealed in the computer program "CHAIRFIT" constitutes a part of the invention and performs these functions.
Lowering and raising the backrest is accomplished by a lever mounted at a fixed point on the back member in many reclining chairs. The present invention, however, employs a 3rd class lever pivotally connected to the frame and sliding on the backrest to raise the backrest. U.S. Pat. No. 3,111,181 discloses a bell crank mounted on the frame which lowers the backrest when the seat moves forward and raises it when it moves rearward. The bell crank is actuated by linkage arms in compression, requiring great strength in the linkage. In the present invention it is common for the seat to move 8.5 to 11.5 inches to locate center of gravity equidistantly between wheels. A bell crank responding to such movement would require two arms. The lower arm's length would minimally exceed 8.5 to 11.5 inches. Such design is characterized by large amounts of space, great weight, and diminished strength and stability.
The present invention is designed so that the backrest and legrest segments may be easily detached from the seat, so that rear legs retract, so that the legs fold on the underside of the frame, and so that the seat may be conveniently detached from the frame if desired. The method of folding the frame is devised such that wheelchair wheels are substantially contained within the folded device and so that wheels do not interfere with motors and supporting devices. Prior art relating to longitudinally folding a seat along is disclosed in U.S. Pat. No. 3,856,345.
The present invention supports the occupant by means of a plurality of adjacent transverse wood-like slats supported by coil compression springs at opposite ends. The program CHAIRFIT determines discrete spring rates for backrest, seat, and legrest such that at an intermediate backrest angel, approximately constant average spring deflection occurs in those three segments. The resulting customized surface contours to body shape, yet accommodates body movement and changing position. Springs and slats have been disclosed for use on beds for a long time, but the method was primitive and has fallen into disuse. It is believed that the prior art does not reveal a method for contouring slats to a chair occupant in a variety of positions. The following U.S. Pat. Nos. are representative of the prior art; U.S. Pat. Nos. 62,395; 67,362; 2,112,702; 3,081,129 and 3,999,234.
The present invention may be used as a rocking chair have been prescribed for presidents Kennedy and Johnson as an adjunct to managing musculoskeletal pain. A joint study by Eastern Virginia Graduate School of Medicine and the Medical College of Virginia supports the conclusion that self sustained rocking chair ventilation can be used in respiratory muscle failure as an alternative to continuous mechanical ventilation. A patient tends to synchronize breathing to the frequency of the rocking motion. Benefits of rockers previously cited include: increased post-treatment Ference's Human Field Motion Test scores, improved restedness based on Smith's Restedness/Tiredness scale, facilitated equilibrium, increased kinesthetic awareness, reduced blood stasis in the lower limbs, reduced constipation, reduced bed sores, dissipated tension, physical therapy, and reduced insomnia.
A further advantage revealed in the present invention is that when a rocker is pivotally attached to a short rear leg and adjustably moved downward at the point at which it is attached to the front leg, seat angle is increased by a substantially greater amount than if the front leg had been equally extended. Altering seat angle by adjusting the rocker arm becomes the preferred method in the present invention. In so far as I am aware prior art does not disclose such use of a rocker.
The individual advantages of the invention constitute significant advances over prior art. Additionally in combination these advantages are synergetic. The infirm and disabled should benefit greatly from its use. It is sufficiently comfortable and has such a wide range of functions that it is fully anticipated that it will also be used by healthy people.